fetus (n.), fetal (adj.)

https://doi.org/10.1351/goldbook.10718

Young mammal within the uterus of the mother, from the visible completion of characteristic organogenesis until birth.

Note: In humans, this period is usually defined as from the third month after fertilization until birth; prior to this the young mammal is referred to as an embryo.
Source:
PAC, 2016, 88, 713. 'Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)' on page 755 (https://doi.org/10.1515/pac-2015-1202)